The generation of a normal immune responses requires the coordinate activation and function of multiple cellular components within the immune system. Deficiencies in one or more of these cellular components can result in diseases ranging from immunodeficiency to autoimmunity. Appropriate function of most immune cells is dependent on the appropriate activation of multiple families of protein tyrosine kinases (PTKs). One such family, the Syk-family of PTKs, has been demonstrated to play a critical role in a wide number of hematopoietic derived cells and has been implicated in the function of a variety of receptors. While much has been learned about the biochemistry and developmental role of the Syk PTK in immune cell development and function, little is known about how Syk regulates cellular activation and biologic outcome. This PPG application will utilize a multi-disciplinary approach to analyze the mechanisms by which Syk regulates B cell and natural killer cell function and development Project 1 will analyze the function of a novel regulatory domain within Syk in B cell antigen receptor activation and dynamics of Syk function in real time. Project 2 will determine the structural requirements within Syk for pre-BCR function during B cell development and will also ask whether alterations in the signaling capacity of the BCR, by expressing Syk enzymes with increased or decreased enzymatic activities, can affect the selection of the BCR repertoire. Project 3 will dissect the function of this family of PTKs in natural killer cell function and development. Insights from each project will enhance the experimental approaches utilized by the other projects. This multi-disciplinary approach will not only provide a more in-depth understanding of how Syk regulates immune cell function, but may also provide insights into how PTKs regulate biological processes. These insights, in turn, may provide mechanistic information that may serve as the basis for more rational therapeutic approaches for drug design for autoimmune diseases and transplantation rejection.